/* version 2024-09-23
 * released in the public domain
 * http://sedcore.eu.org/raspi/lcd
 */

/* gcc -Wall main.c -o lcd -lpigpio */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pigpio.h>

/* change those values to fit your settings */
/* broadcom numbering */
#define GPIO_RS 26
#define GPIO_E  19
#define GPIO_D4 13
#define GPIO_D5  6
#define GPIO_D6  5
#define GPIO_D7 11

/* register selection */
#define RS_CONTROL 0
#define RS_DATA    1

/* instruction table */
#define CLEAR_DISPLAY   0x01
#define RETURN_HOME     0x02
#define ENTRY_MODE_SET  0x04
#define DISPLAY_CONTROL 0x08
#define SHIFT_CONTROL   0x10
#define FUNCTION_SET    0x20
#define SET_CGRAM_ADDR  0x40
#define SET_DDRAM_ADDR  0x80

int init_gpio(void)
{
  if (gpioSetMode(GPIO_RS, PI_OUTPUT) != 0) goto err;
  if (gpioSetMode(GPIO_E,  PI_OUTPUT) != 0) goto err;
  if (gpioSetMode(GPIO_D4, PI_OUTPUT) != 0) goto err;
  if (gpioSetMode(GPIO_D5, PI_OUTPUT) != 0) goto err;
  if (gpioSetMode(GPIO_D6, PI_OUTPUT) != 0) goto err;
  if (gpioSetMode(GPIO_D7, PI_OUTPUT) != 0) goto err;
  return 0;
err:
  printf("gpioSetMode failed\n");
  return -1;
}

int gpio_end()
{
  if (gpioWrite(GPIO_E, 0) != 0) goto err;
  if (gpioWrite(GPIO_RS, 0) != 0) goto err;
  if (gpioWrite(GPIO_D4, 0) != 0) goto err;
  if (gpioWrite(GPIO_D5, 0) != 0) goto err;
  if (gpioWrite(GPIO_D6, 0) != 0) goto err;
  if (gpioWrite(GPIO_D7, 0) != 0) goto err;
  return 0;
err:
  printf("gpioWrite failed\n");
  return -1;
}

void nsleep(int ns)
{
  struct timespec t;
  t.tv_sec = ns / 1000000000;
  t.tv_nsec = ns % 1000000000;
  if (nanosleep(&t, NULL) == -1)
    printf("nanosleep failed, expect display errors\n");
}

int put_nibble(int rs, int data)
{
  int d4 = (data >> 0) & 1;
  int d5 = (data >> 1) & 1;
  int d6 = (data >> 2) & 1;
  int d7 = (data >> 3) & 1;

  if (gpioWrite(GPIO_RS, rs) != 0) goto err;
  if (gpioWrite(GPIO_D4, d4) != 0) goto err;
  if (gpioWrite(GPIO_D5, d5) != 0) goto err;
  if (gpioWrite(GPIO_D6, d6) != 0) goto err;
  if (gpioWrite(GPIO_D7, d7) != 0) goto err;

  /* tsu1 is 50 nanoseconds */
  int tsu1 = 50;
  nsleep(tsu1);
  if (gpioWrite(GPIO_E, 1) != 0) goto err;
  /* tw is 230 nanoseconds, but let's use 250, tiny margin for why not */
  int tw = 250;
  nsleep(tw);
  if (gpioWrite(GPIO_E, 0) != 0) goto err;
  /* tc is 500 nanoseconds, let's sleep what remains after tw */
  int tc_remain = 500 - tw;
  nsleep(tc_remain);

  return 0;

err:
  printf("put_nibble failed\n");
  return -1;
}

int put_byte(int rs, int data)
{
  if (put_nibble(rs, (data >> 4) & 0xf) != 0) goto err;
  if (put_nibble(rs, data & 0xf) != 0) goto err;
  return 0;

err:
  printf("put_byte failed\n");
  return -1;
}

int init_lcd(void)
{
  int v;
  /* We don't know what's the state of the lcd at this point
   * (4 or 8 bits bus mode, if 4 bits: lcd waiting for bits d3-d0 or d7-d4).
   * So to be sure, let's go to 8 bits bus mode.
   * If the lcd is in 4 bits bus mode and waiting
   * for d3-d0, we need to write xxxx then 0x03 in d7-d4 then xxxx for d3-d0.
   * If 4 bits bus mode and waiting for d7-d4, we need to write 0x03 in d7-d4
   * then xxxx for d3-d0.
   * If 8 bits mode, nothing is needed, but writing 0x03 (in d7-d4, which is
   * what we do; d3-d0 is not plugged, value is whatever, we don't care) is
   * ok. Writing it two or three times is also ok.
   * Mix all cases and you find out that writing 0x03 (in d7-d4) three times
   * will put the lcd in 8 bits bus mode whatever the starting state.
   */
  if (put_nibble(RS_CONTROL, 0x03)) goto err;
  usleep(39);
  if (put_nibble(RS_CONTROL, 0x03)) goto err;
  usleep(39);
  if (put_nibble(RS_CONTROL, 0x03)) goto err;
  usleep(39);
  /* Now, we are in 8 bits bus mode, let's switch to 4 bits bus mode
   * by outputting 0x02 in d7-d4 (with only one write, so by using
   * put_nibble(), not put_byte()).
   */
  if (put_nibble(RS_CONTROL, 0x02)) goto err;
  usleep(39);
  /* and now we're good, 4 bits bus mode, we can init */

  /* function set */
  int dl = 0;  /* 0: 4 bits bus mode, 1: 8 bits bus mode */
  int n = 1;   /* 0: 1 line mode, 1: 2 lines modes */
  int f = 0;   /* 0: 5x8 dot format, 1 : 5x11 dot format */
  v = FUNCTION_SET | (dl << 4) | (n << 3) | (f << 2);
  if (put_byte(RS_CONTROL, v)) goto err;
  usleep(39);

  /* display on/off control */
  int d = 1;  /* display on/off */
  int c = 0;  /* cursor on/off */
  int b = 0;  /* blink on/off */
  v = DISPLAY_CONTROL | (d << 2) | (c << 1) | b;
  if (put_byte(RS_CONTROL, v)) goto err;
  usleep(39);

  /* display clear */
  if (put_byte(RS_CONTROL, CLEAR_DISPLAY)) goto err;
  usleep(1530);

  /* entry set mode */
  int id = 1;      /* 0: decrement mode, 1: increment mode */
  int sh = 0;      /* 0: entire shift off, 1: entire shift on */
  v = ENTRY_MODE_SET | (id << 1) | sh;
  if (put_byte(RS_CONTROL, v)) goto err;
  usleep(39);

  /* init sequence ends here */

  /* let's return home */
  if (put_byte(RS_CONTROL, RETURN_HOME)) goto err;
  usleep(1530);

  return 0;

err:
  printf("init_lcd failed\n");
  return -1;
}

void clear_screen(void)
{
  /* display clear */
  if (put_byte(RS_CONTROL, CLEAR_DISPLAY)) goto err;
  usleep(1530);

  /* return home */
  if (put_byte(RS_CONTROL, RETURN_HOME)) goto err;
  usleep(1530);

  return;

err:
  printf("clear_string failed\n");
}

void put_string(char *s, int l)
{
  /* go to beginning of line l (l=0 for first line, l=1 for second line) */
  int address = l * 0x40;
  int v = SET_DDRAM_ADDR | address;
  if (put_byte(RS_CONTROL, v)) goto err;
  usleep(39);

  /* no check on string size, caller's business */
  while (*s) {
    if (put_byte(RS_DATA, *s)) goto err;
    usleep(43);
    s++;
  }

  return;

err:
  printf("put_string failed\n");
}

void usage(void)
{
  printf("[options] [string]\n");
  printf("options:\n");
  printf("    -clear\n");
  printf("        clear screen before anything else\n");
  printf("    -l <line>\n");
  printf("        choose line, 1 or 2, default 1\n");
  printf("    -no-init\n");
  printf("        don't init LCD (for eg. it was already done)\n");
  exit(1);
}

int main(int n, char **v)
{
  int r;
  int line = 0;
  int do_clear = 0;
  int do_init = 1;
  char *s = NULL;

  for (int i = 1; i < n; i++) {
    if (!strcmp(v[i], "-h") || !strcmp(v[i], "--help")) usage();
    if (!strcmp(v[i], "-clear")) { do_clear = 1; continue; }
    if (!strcmp(v[i], "-l")) { if (i >= n-2) usage(); line = atoi(v[++i]) - 1; continue; }
    if (!strcmp(v[i], "-no-init")) { do_init = 0; continue; }
    if (s) usage();
    s = v[i];
  }

  if (line != 0 && line != 1) usage();

  r = gpioInitialise();
  if (r < 0) { printf("gpio lib init error\n"); exit(1); }

  if (init_gpio() != 0) goto end;
  if (do_init) {
    if (init_lcd() != 0) goto end;
  }

  if (do_clear) clear_screen();
  if (s != NULL) put_string(s, line);

  /* clear GPIO output pins (set them to 0) */
  gpio_end();

end:
  gpioTerminate();

  return 0;
}